Vehicle restraint with bi-directional sensor

ABSTRACT

A vehicle restraint restricts the movement of a vehicle at a loading dock by engaging the vehicle&#39;s RIG (rear impact guard). The vehicle restraint includes a barrier carried by a vertically translatable track follower, the barrier being driven by a motor or some other type of power unit. A RIG sensor detects the RIG&#39;s horizontal position relative to the barrier and can periodically energize the motor to maintain the barrier in generally continuous contact with the RIG, even if the RIG moves horizontally away from the barrier. Detection of such horizontal movement of the RIG triggers the barrier to move accordingly to reduce a horizontal gap that may have formed between the RIG and the barrier.

FIELD OF THE DISCLOSURE

The present disclosure generally pertains to a vehicle restraint thatengages a truck's rear impact guard (RIG) to help prevent the truck frominadvertently pulling away from a loading dock. More specifically, to avehicle restraint that senses horizontal movement of the RIG andresponds to the sensing by helping to ensure that the restraint is in anacceptable horizontal position relative to the RIG.

BACKGROUND

When loading or unloading a truck parked at a loading dock, it isgenerally a safe practice to help restrain the truck from accidentallymoving too far away from the dock. This is often accomplished by avehicle restraint that engages what is referred to, in the industry, asa truck's ICC bar (Interstate Commerce Commission bar) or RIG (RearImpact Guard). An ICC bar or RIG is a bar or beam that extendshorizontally across the rear of a truck, below the truck bed. Itsprimary purpose is to help prevent an automobile from under-riding thetruck in a rear-end collision. A RIG, however, also provides aconvenient structure for a vehicle restraint to engage, therebyobstructing the bar's (and thus, the truck's) movement away from thedock. To release the truck, at least a portion of the restraint islowered to a stored position below the bar, which also allows the nexttruck to back into the dock.

There are at least two general types of RIG-engaging vehicle restraints.A first type of RIG-engaging vehicle restraint relies on the power ofthe truck backing into the dock as the impetus for operating the vehiclerestraint. This type of vehicle restraint may use spring force forstoring the restraint in a normally raised position. As a truck backsits RIG over the upwardly biased vehicle restraint, the RIG engages aramp or some other type of mechanical actuator that forces the restraintdown, underneath the RIG. When the truck's RIG is properly positionedover the restraint, a relatively small power unit can be actuated toraise a barrier portion of the restraint in front of the RIG. Examplesof such truck-powered vehicle restraints that store in a normally raisedposition are disclosed in U.S. Pat. Nos. 6,190,109; 6,322,310;5,882,167; 5,702,223 and 5,297,921, all of which are specificallyincorporated by reference herein.

In addition to utilizing the truck's power to operate the vehiclerestraint, the spring of such restraints also enables upwardly biasedrestraints to follow the incidental vertical movement of the RIG as thetruck is being loaded or unloaded of its cargo. This can be advantageousin comparison to other types of vehicle restraints.

A second general type of vehicle restraint stores in a lowered positionand typically requires some type of power unit, such as a motor orhydraulic cylinder, to raise the restraint to an elevation where it cancapture the RIG. Since the power unit must raise the entire movingportion of the vehicle restraint, lifting such weight may require apower unit of substantial size and horsepower, which can add even moreweight to the restraint. The power unit of this vertically movingrestraint may include a small spring, or other mechanism, to accommodateslight vertical movement of the truck/RIG, but a vehicle restraint ofthis type typically has no mechanism for accommodating horizontalmovement of the RIG.

A limitation common to both types of restraint is an inability of therestraint to follow the horizontal movement of the RIG. For example,after a vehicle restraint is initially positioned relative to the RIG,the loading or unloading operation may cause the truck to move bothvertically and horizontally. The vehicle restraint's barrier preventsthe RIG from moving forward horizontally, in a direction opposite thedock face, but it does not generally accommodate the RIG moving backwardin a horizontal direction toward the dock face (away from therestraint's raised barrier). This can leave a horizontal gap between theRIG and the barrier even though the spring or actuator allows forvertical movement and continues to hold the restraint tightly up againstthe underside of the RIG. If the vehicle later begins to return to itsmore forward position, the gap provides a backlash in which the RIG canaccelerate before striking the barrier with an impact that may besufficient to bend or otherwise damage the RIG. In the case of apremature truck/trailer departure, this horizontal gap may actuallyallow a trailer to build up enough momentum to “jump” over the barrierprior to the operator lowering the restraint and releasing the trailer.

Known prior art restraints included no means for detecting thehorizontal position of the RIG relative to the vehicle restraint'sbarrier. Because the RIG's horizontal position relative to the barrierwas not detected, prior art restraints did nothing to eliminate thepotentially hazardous horizontal gap that may result from the backwardmovement of the trailer (and RIG), nor did they do anything to alertworkers of such a hazardous condition. Consequently, a need exists for avehicle restraint that can properly respond not only to verticalmovement of a RIG but also to horizontal movement of a RIG to warn of,and preferably minimize, a gap that may form between the barrier and theRIG upon horizontal movement of the RIG.

SUMMARY

In order to provide a vehicle restraint that can properly respond tohorizontal movement of a RIG, a restraint disclosed herein includes asensor that detects whether a RIG has moved horizontally away from therestraint's barrier.

In some examples, the vehicle restraint includes a barrier that canrotate to take up both horizontal and vertical slack between the barrierand a RIG.

In some examples, the vehicle restraint includes a dual-plate barrierwith a RIG sensor protectively interposed between the two plates.

In some examples, the RIG sensor includes an optical device.

In some examples, the RIG sensor includes a pivotal arm.

In some examples, a spring moves the vehicle restraint in response tovertical movement of the RIG, and a motor moves the restraint's barrierin response to horizontal movement of the RIG.

In some examples, a spring biases the vehicle restraint upward, and amotor rotates the restraint's barrier between a protruding blockingposition and a retracted stored position.

In some examples, the vehicle restraint is a vertically moving restraintthat includes a sensor to detect whether a RIG has moved horizontallyaway from a barrier included on the restraint.

In some examples, the vertically moving restraint responds to the sensordetecting that the RIG has moved horizontally away from a barrier bytriggering a signaling system.

In some examples, the vertically moving restraint responds to the sensordetecting that the RIG has moved horizontally away from a barrier bymoving the barrier horizontally toward the RIG.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a right side view of a vehicle restraint with its trackfollower raised and its barrier in a stored position.

FIG. 2 is a right side view of the vehicle restraint of FIG. 1 butshowing a vehicle lowering the track follower.

FIG. 3 is a right side view of the vehicle restraint of FIG. 1 butshowing the vehicle's RIG on top of the track follower.

FIG. 4 is a right side view similar to FIG. 3 but showing the barrier atits blocking position.

FIG. 5 is a right side view similar to FIG. 4 but showing the RIG havingmoved away from the barrier.

FIG. 6 is a right side view similar to FIG. 5 but showing the vehiclerestraint's response to the RIG's horizontal movement away from thebarrier.

FIG. 7 is a front view of FIG. 1 but with a ramp extension omitted toshow other features of the restraint more clearly.

FIG. 8 is a right side view similar to FIG. 3 but illustrating analternate example.

FIG. 9 is a right side view showing another operating position of thevehicle restraint of FIG. 8.

FIG. 10 is a right side view showing another operating position of thevehicle restraint of FIG. 8.

FIG. 11 is a right side view showing another operating position of thevehicle restraint of FIG. 8.

FIG. 12 is a right side view showing another operating position of thevehicle restraint of FIG. 8.

FIG. 13 is a right side view showing another operating position of thevehicle restraint of FIG. 8.

FIG. 14 is a right side view similar to FIG. 3 but illustrating yetanother example.

FIG. 15 is a right side view showing another operating position of thevehicle restraint of FIG. 14.

FIG. 16 is a right side view of a vertically moving vehicle restraintwith its track follower lowered and its barrier assembly in a storedposition.

FIG. 17 is a right side view of the vehicle restraint of FIG. 16 butshowing the vehicle's RIG engaged by the barrier assembly, wherein thebarrier assembly is in its blocking position.

FIG. 18 is similar to FIG. 17, but shows an enlarged view of the barrierassembly in its blocking position.

FIG. 19 is similar to FIG. 18, but shows another mechanism forhorizontally positioning the barrier.

DETAILED DESCRIPTION

To help prevent a vehicle 10 (e.g., truck, trailer, etc.) fromaccidentally pulling too far away from a dock face 12 of a loading dock14, a vehicle restraint 16 includes a barrier 18 for engaging orcapturing a RIG 20, or ICC bar, of vehicle 10 as the vehicle is beingloaded or unloaded of its cargo. Because vehicle 10 typically has someincidental movement during loading and unloading operations, vehiclerestraint 16 includes a RIG sensor 22 and other structure that enablesrestraint 16 to properly respond to such movement. FIGS. 1-6 are rightside views illustrating the operating sequence of vehicle restraint 16,and FIG. 7 is a front view of FIG. 1 (looking toward dock face 12). Aramp extension 24 is omitted in FIG. 7 to show other features ofrestraint 16 more clearly.

To vertically position vehicle restraint 16 relative to RIG 20,restraint 16 comprises a track follower 26 that is movable between araised position (FIGS. 1 and 7) and various lowered positions (FIGS.2-6). The vertical movement of track follower 26 is guided by a track 28that can be mounted to dock face 12. A tension spring 30, or some othertype of resilient member, biases track follower 18 to its raisedposition (FIGS. 1 and 7), thus urging track follower 26 up against theunderside of RIG 20 when RIG 20 is positioned above track follower 26 asshown in FIGS. 3-6.

In order to capture RIG 20 and thus limit its movement away from dockface 12, track follower 26 carries rotatable barrier 18 that a powereddrive unit 32 (e.g., an electric motor, hydraulic motor,piston/cylinder, etc.—see FIG. 7) can rotate between a stored position(FIGS. 1, 2, 3 and 7) and various blocking positions (FIGS. 4, 5 and 6).

Although the actual operation of vehicle restraint 16 may vary, FIGS.1-6 illustrate an example. Operation may begin as shown in FIG. 1, wherevehicle 10 is backing into dock 14 while track follower 26 is at itsraised position, and barrier 18 is at its stored position.

In FIG. 2, vehicle 10 continues backing into dock 14, which forces RIG20 to slide over a ramp 34 or to engage some other type of mechanicalstructure that enables vehicle 10 to force track follower 26 downunderneath RIG 20. In this example, the interaction between ramp 34 andRIG 20 forces track follower 26 downward against the upward urging ofspring 30.

In FIG. 3, vehicle 10 is shown having backed RIG 20 over track follower26 such that RIG 20 passes over the top of a distal end 36 of barrier18. RIG 20 is now in a position where barrier 18 can rise to capture RIG20.

In FIG. 4, power unit 32 (FIG. 7) rotates barrier 18 from its storedposition to a blocking position to help contain RIG 20 at a locationthat ensures a certain amount of lip purchase 42 or overlap between alip 38 of a conventional dock leveler 40 and a rear edge 44 of vehicle10. Once barrier 18 rises to its blocking position, dock leveler 40 canbe operated in a conventional manner to set lip 38 upon the vehicle'struck bed as shown in FIG. 4.

Although the initial energizing of power unit 32 to raise barrier 18could be done automatically in response to some type of sensor thatsenses the arrival of vehicle 10 or RIG 20, in some cases the initialenergizing of power unit 32 is simply triggered by a conventionalmanually operated switch. Once energized, power unit 32 continuesraising barrier 18 until RIG sensor 22 determines that RIG 20 is withina RIG-receiving throat area 44, or preferred capture area, of barrier18. Once RIG sensor 22 determines that RIG 20 is within theRIG-receiving throat area 22, or preferred capture area, power unit 32is de-energized, thereby stopping upward movement of barrier 18. RIGsensor 22 may also be electrically coupled with a signaling system(e.g., visual or audible communication means) to alert interestedparties of the position of the barrier relative to the RIG. Thisarrangement may offer some advantages over prior art rotating hookrestraints.

Prior art rotating hook restraints typically included a timer that wasstarted at the same time the power unit was triggered. The power unitwas then energized for a pre-determined period of time, after which thetimer cut power to the power unit. The timer's period of time was set asthe period of time necessary to ensure that the hook would rotate enoughto properly capture the highest RIG in a given service range. If the RIGwas lower in elevation, though, the hook would engage the RIG before thetimer expired. Because the timer had not expired, the power unit wouldcontinue to be energized, even though the hook could not move anyfurther (contact with the RIG prevented further movement). Thisarrangement required the use of a slip clutch to prevent damage to thesystem components during the period of time in which the power unitcontinued to be energized although the hook could move no further.Because this type of rotating hook restraint did not rely on theposition of the RIG relative to the restraint, proper RIG-restraintengagement was indirectly measured by detecting the rotational positionof the restraint hook. For example, U.S. Pat. No. 4,267,748 discloses afinger or cam attached to the shaft of the rotating hook. When the shaftwas rotated, raising the hook to an operational position, the finger orcam would engage a switch, thereby indicating that the hook was in itsoperational position. As described, this type of system only detects therotational position of the restraint hook, not the hook's actualposition relative to the RIG. Accordingly, prior to the currentinvention, a rotating hook vehicle restraint's actual engagement withthe RIG was not directly sensed or indicated.

By sensing the actual presence of the rotating hook in a preferredcapture area, the current restraint may reduce wear on the power unit,and it may eliminate the need for a timer and a slip clutch, along withother benefits. Although the actual design of RIG sensor 22 may vary,the sensor will provide the aforementioned benefits. In some examples,RIG sensor 22 comprises a sensing arm 46 pivotally coupled to barrier 18by way of a shaft 48 or some other pivotal connection. RIG sensor 22 mayfurther comprise a spring 50, a mechanical stop 52, and a limit switch54 (proximity switch, electromechanical switch, etc.). In this exampleof RIG sensor 22, arm 46 can pivot between mechanical stop 52 and switch54, while spring 50 biases arm 46 toward stop 52. Switch 54 provides amake or break signal 56 (FIG. 7) whose on/off states are determined bywhether arm 46 is adjacent switch 54.

In FIG. 3, arm 46 is up against stop 52, so signal 56 allows power unit32 to be energized via the manually operated switch mentioned earlier.Once energized, barrier 18 continues to rise until the engagementbetween arm 46 and RIG 20 forces arm 46 to trigger switch 54. Thiscauses switch 54 to change state such that signal 56 now de-energizespower unit 32 to stop barrier 18 at its blocking position of FIG. 4.Accordingly, by detecting the actual position of the RIG relative to thebarrier, the current restraint may reduce wear on the power unit (itdoes not run when the hook is in contact with the RIG) and may eliminatethe need for a timer and a slip clutch.

With barrier 18 restraining RIG 20 and lip 38 safely resting upon thevehicle's truck bed, as shown in FIG. 4, vehicle 10 can now be safelyloaded or unloaded of its cargo using dock leveler 40 as a bridge forpersonnel and material handling equipment to travel to and from vehicle10. Switch 54 and signal 56 can also be electrically coupled to asignaling system, such as lights or audible alarms. For example,engagement between arm 46 and RIG 20 forces arm 46 to trigger switch 54,thereby causing it to change state such that signal 56 changes a lightinside the loading dock from red to green, indicating that the vehiclecan now be safely loaded or unloaded. By measuring the actual positionof the restraint relative to the RIG, a “false lock” indication, basedonly on the rotational position of the restraint, can be effectivelyavoided. Although a lighting system may be the most common means ofcommunicating a proper position of the restraint relative to the RIG todock workers, other forms of communication, or signaling, could readilybe incorporated into the system.

After the restraint is properly positioned relative to the RIG, thevehicle may be safely loaded or unloaded. As cargo or the weight ofmaterial handling equipment is added or removed from the vehicle's truckbed, the vehicle's suspension may allow vehicle 10 to rise and descendaccordingly. Track follower 26 can readily follow such vertical movementand stay in contact with the underside of RIG 20 by virtue of spring 30,which urges track follower 26 upward.

In the position shown in FIG. 4, distal end 36 of barrier 18 is ahorizontal distance 58 from track 28. According to an advantageousfeature of this design, the length of distance 58 may vary. Vehicle 10,for instance, could subsequently move horizontally away from itsposition shown in FIG. 4 to its position shown in FIG. 5 where RIG 20 isup against a dock bumper 60. To eliminate the horizontal gap betweenbarrier 18 and RIG 20, the depicted restraint can sense the gap andre-position barrier 18 to eliminate it. In this example, the horizontalmovement would allow arm 46 to return to its position against stop 52,whereby signal 56 would re-energize power unit 32 to once again rotatebarrier 18 toward RIG 20. Barrier 18 would continue rotating until RIG20 forces arm 46 away from stop 52 to re-trigger switch 54, wherebysignal 56 would then stop barrier 18 at its newly adjusted blockingposition of FIG. 6. Horizontal distance 58′ of FIG. 6 is less thandistance 58 of FIG. 5, so RIG 20 is more constrained in FIG. 6 than inFIG. 5. Reducing or eliminating the horizontal backlash of RIG 20 withinrestraint 16 may reduce the possibility of RIG 20 hammering againstbarrier 18 in an early departure situation. Thus, the barrier systemaccording to one example provides sensing based on the actual presenceof a RIG relative to the barrier, as opposed to sensing based on therotational position of the hook. Put slightly differently, the barriersystem disclosed herein detects the presence of the RIG in a preferredcapture area, wherein the preferred capture area is an area in which thebarrier is horizontally adjacent the RIG. In the case of a rotating hookrestraint, the preferred capture area may also be referred to in the artas a RIG-receiving throat area. Furthermore, sensing that the RIG is notin the preferred capture area may also cause corrective action and/orsignaling.

Automatically repositioning the barrier in response to detecting thatthe RIG has moved horizontally away from the barrier offers numerousbenefits, but it may not be desirable in all circumstances. For example,if the restraint rarely loses contact with the RIG, then it may besufficient to sound an alarm or otherwise signal the loss of contact,wherein this alarm or signal alerts an operator that he must take action(e.g., push a button) to move the restraint horizontally toward the RIG.In this manner, the restraint system detects that the RIG has moved awayfrom the barrier and triggers an alarm to alert a dock worker of apotentially unsafe condition that he should take steps to remedy.

Although these functions could be accomplished by various structures,FIGS. 1-7 illustrate one example. In the illustrated example, trackfollower 26 comprises two side plates 26 a and 26 b attached to a base62. Rollers 64 or slide members extending from side plates 26 a and 26 band protruding into two vertical channels of track 28 help guide thevertical movement of track follower 26. To urge track follower 26upward, one or more springs 30 extend between base 62 and an upperanchor 66 affixed to track 28. Although barrier 18 could be a singlehook-shaped member, barrier 18 comprises two plates 18 a and 18 b thathelp protect RIG sensor 22 therebetween. Plates 18 a and 18 b can bekeyed to shaft 48 to provide a positive drive connection to drive unit32. A chain 68 and two sprockets 70 and 72 can couple the output ofdrive unit 32 to shaft 48. For overload protection, a slip clutch 74 canbe installed somewhere in the drive train between shaft 48 and driveunit 32, although the current sensing configuration may allow the slipclutch to be eliminated. One end 74 of spring 50 can be attached toplate 18 b, and an opposite end 76 can be attached to arm 46. Stop 52can be a pin or some other suitable structure extending from barrier 18.At least part of RIG sensor 22 can be attached at an appropriatelocation on barrier 18. Restraint 16 also may include a barrier sensor78 coupled to track follower 26. Barrier sensor 78 provides astored-signal 80 (FIG. 7) that triggers powered drive unit 32 to stoplowering barrier 18 when the barrier reaches its stored position.

In the example of FIGS. 1-7, barrier 18 is keyed or otherwise solidlyfixed to shaft 48 while arm 46 can rotate about shaft 48. In analternate example, however, generally the opposite is true. Morespecifically, FIGS. 8-13 show a vehicle restraint 82 whose barrier 84can rotate relative to a shaft 86, but an arm 88 is rigidly fixed toshaft 86. A tension spring 90, which extends between arm 88 and barrier84, urges barrier 84 upward relative to arm 88. In this case, spring 90is sufficiently strong to support the barrier's weight. The operation ofvehicle restraint 82 may be as follows:

FIG. 8 corresponds to FIG. 3. Vehicle 10 just placed its RIG 20 uponvehicle restraint 82. Barrier 84 is at its stored position, and arm 88is resting upon stop member 91. The tension in spring 90 holds barrier84 slightly above arm 88.

In FIG. 9, drive unit 32 (FIG. 7) is raising arm 88 via shaft 86, andbarrier 84 rises with arm 88 due to spring 90.

In FIG. 10, barrier 84 makes initial contact with RIG 20; however, driveunit 32 (FIG. 7) continues raising arm 88 because arm 88 has not yettripped switch 54.

FIG. 11 shows arm 88 having tripped switch 54, which de-energizes powerunit 32 (FIG. 7). The tripping of switch 54 indicates that RIG 20 is inthe preferred capture area, that is, properly positioned relative tobarrier 84. Tripping of switch 54 may also trigger an associatedsignaling system (lights, sound, or other) to communicate that the RIGis in the preferred capture area and the loading or unloading operationmay commence. At this point vehicle restraint 82 remains substantiallystationary as long as RIG 20 remains still. In this situation, thetension in spring 90 causes barrier 84 to maintain some springloaded-pressure against RIG 20. To prevent RIG 20 from forcing barrier84 down past the elevation of arm 88, barrier 84 includes a stop block55 that limits the relative rotation between barrier 84 and arm 88.

If RIG 20 moves slightly closer to dock face 12, as shown in FIG. 12,barrier 84 will tend to follow that movement due to the urging of spring90. If the movement of RIG 20 and the relative movement of arm 88 aresmall, such that RIG 20 remains in the preferred capture area, thenbarrier 84 may be able to follow the RIG's movement without drive unit32 having to be re-energized by switch 54. If, however, the movement ofRIG 20 and the relative movement of arm 88 are sufficient to trip switch54, indicating that a horizontal gap has developed between barrier 84and RIG 20 (i.e., RIG 20 has moved out of the preferred capture area),then drive unit 32 is re-energized by switch 54 to force arm 88 andbarrier 84 back up against the RIG, in its new position, as shown inFIG. 13. Thus, vehicle restraint 82 can closely follow incidentalmovement of RIG 20 by spring force alone and follow greater movement byautomatically energizing power unit 32 when a horizontal gap formsbetween barrier 84 and RIG 20 such that RIG 20 moves out of thepreferred capture area. With this design, drive unit 32 could beenergized less often. Also, arm 88 never needs to actually contact RIG20, so arm 88 could be completely hidden inside or underneath barrier84. Furthermore, because the position of the restraint relative to theRIG is actually measured, the signaling system (lights or other) can bemore accurate, allowing the system to more effectively alert dockworkers of a potentially unsafe condition.

FIGS. 14 and 15 illustrate yet another example of a vehicle restraint 92that is similar vehicle restraint 16 of FIGS. 1-7, wherein FIGS. 14 and15 correspond to FIGS. 3 and 4 respectively. With vehicle restraint 92,RIG sensor 22 is replaced by an optical beam 94 or comparableelectromagnetic field emitted and/or received by a field type sensor 96mounted to a barrier 98. A beam reflector 100 may or may not be neededdepending on the chosen style of sensor 96. With vehicle restraint 92,the presence of RIG 20 in the preferred capture area can be detected byRIG 20 interrupting beam 94 rather than by displacing arm 46.

Yet another example of a vehicle restraint 102 is shown in FIGS. 16-18.Like the previous examples, vehicle restraint 102 is intended to helpprevent a vehicle 10 (e.g., truck, trailer, etc.) from accidentallypulling too far away from a dock face 12 of a loading dock 14. As in theprevious examples, the actual position of the RIG relative to thevehicle restraint's barrier is sensed, with the barrier position beingaltered, if the barrier moves out of the preferred capture area, tobring the barrier back into a proper position relative to the RIG.However, unlike the previous examples, vehicle restraint 102, as shownin FIGS. 16-18, does not rely on an upwardly-biased, rotating hookvehicle restraint to provide a barrier to vehicle movement, insteadrelying on a vertically-moving barrier assembly 104. Barrier assembly104 comprises a barrier 114, a sliding barrier 116, a RIG sensor 118, aRIG sensor extension 122, and a RIG sensor switch 124. FIGS. 16-18 areright side views illustrating the operating sequence of vehiclerestraint 102.

FIG. 16 shows barrier assembly 104 in a stored position, wherein thebarrier assembly is protected by housing 106. Barrier assembly positionsensor 108 is also protected by housing 106 and senses when barrierassembly 104 is in its stored position. After vehicle 10 is backed intoa loading/unloading position against loading dock bumper 60, as shown inFIG. 17, the vehicle restraint may be actuated, energizing liftingcylinder 110 and causing it to extend. As lifting cylinder 110 extends,it exerts a force against barrier assembly 104 causing rollers 112 totravel upward within roller track 134, which can be mounted to dock face12. Barrier assembly 104 can be attached to rollers 112 such thatbarrier assembly 104 moves with rollers 112. Barrier assembly 104continues to travel upward until barrier 114 contacts RIG 20. Contactwith RIG 20 prevents barrier assembly 104 from moving any furtherupward, thereby causing the pressure in lifting cylinder 110 to rise.Once the internal pressure of lifting cylinder 110 reaches apre-determined threshold, a second cylinder, sliding cylinder 120, isenergized. Once energized, sliding cylinder 120 retracts, causingsliding barrier 116 to move horizontally toward dock face 12. Slidingbarrier 116 moves horizontally toward dock face 12 until RIG sensor 118contacts RIG 20. RIG sensor 118 is pivotally mounted to sliding barrier116 and biased to the rest position shown in FIG. 16, such thatcontinued horizontal movement of sliding barrier toward dock face 12causes RIG sensor 118 to rotate until RIG sensor extension 122 actuatesRIG sensor switch 124. RIG sensor switch can be a magnetic proximityswitch, a physical contact switch, or one of a variety of other switchesknown and used by those of ordinary skill in the art. Actuation of RIGsensor switch 124 indicates that the RIG is in a preferred capture area,wherein preferred capture area refers to a position in which the RIG ishorizontally adjacent the barrier. When RIG sensor switch 124 detectsthat the RIG is in a preferred capture area, it causes both slidingcylinder 120 and lifting cylinder 110 to cease extending, resulting inthe barrier assembly in the engaged position shown in FIGS. 17 and 18.Furthermore, RIG sensor switch 124 may also be electrically coupled to asignaling system (lights, sound, or other) to accurately communicateinformation about the position of the restraint relative to the RIG tointerested parties.

As shown best in FIGS. 17 and 18, sliding barrier 116 includes anextension tip 126 that extends over the top of a portion of the RIG.Like the rotating hook restraint shown in FIGS. 1-15, but unlike atraditional vertically-moving barrier, extension tip 126 provides abarrier to upward movement of the RIG. Thus, in the event that thetrailer's landing gear collapses, extension tip 116 will help preventthe RIG (and the rear of the trailer) from rapidly moving upward. Asdetailed above, RIG sensor 118 acts to ensure that RIG 20 isconsistently positioned relative to sliding barrier 116 and extensiontip 126 (with RIG 20 in the preferred capture area), such that extensiontip 126 extends over a portion of RIG 20.

As a fork truck enters and exits the trailer during theloading/unloading operation, the trailer (and the RIG) tends to movevertically, movement that is often referred to as trailer “float.” Toallow barrier assembly 104 to follow RIG 20 as it floats slightly, thelower end 130 of lifting cylinder 110 is slidably mounted and attachedto float spring 128. If RIG 20 moves slightly downward, float spring 128allows barrier assembly 104 to follow such movement, and if RIG 20 movesback upward to its original position, float spring 128 urges barrier 114upward, in contact with RIG 20. Thus, if the RIG moves a relativelysmall amount, barrier assembly 104 may be able to follow the RIG'smovement without the need for lifting cylinder 110 to be re-energized.

However, vertical movement of the RIG is typically accompanied byhorizontal movement of the RIG. If RIG 20 moves horizontally closer todock face 112, then a horizontal gap would result between the barrierand RIG 20, such that RIG 20 may no longer be in the preferred capturearea. According to an advantageous feature of this design, this gap maybe sensed and minimized or eliminated. That is, for such horizontal RIGmovement, RIG 20 may lose contact with RIG sensor 118, resulting in RIGsensor 118 returning to its rest position and RIG sensor extension 122losing contact (e.g., magnetic contact or physical contact) with RIGsensor switch 124. When engagement between RIG sensor extension 122 andRIG sensor switch 124 is lost (indicating that the RIG is no longer inthe preferred capture area), lifting cylinder 110 is re-energized and,once its internal pressure reaches the pre-determined level (as detailedabove), sliding cylinder 120 is re-energized. Re-energizing slidingcylinder 120 causes it to retract, which, in turn, causes slidingbarrier 116 to move horizontally toward dock face 12 to minimize thehorizontal gap that has formed between RIG 20 and sliding barrier 116.Sliding barrier continues to move horizontally until RIG sensor 118contacts RIG 20 and RIG sensor extension 122 is re-engaged with RIGsensor switch 124. Barrier assembly 104 is thereby returned to itsengaged position, wherein RIG 20 is in the preferred capture area. Thus,RIG sensor 118 helps ensure that RIG 20 is consistently and properlypositioned relative to sliding barrier 116 and extension tip 126 (i.e.,in the preferred capture area). Furthermore, RIG sensor 118 can beelectrically coupled to a means for accurately signaling (via lights,sound, or other) when the RIG is properly positioned relative to thebarrier assembly. If lights are used to signal, these lights may changestate (e.g., change illuminated color, temporarily flash) until the RIGreturns to the preferred capture area. Alternatively, a horn could soundin response to RIG sensor 118 losing contact with the RIG. In fact, ifthe restraint rarely loses contact with the RIG, then it may besufficient to sound an alarm or otherwise signal the loss of contact,wherein this alarm or signal alerts an operator that he must take action(e.g., push a button) to move the restraint horizontally toward the RIG.

As described, when the RIG is properly positioned relative to thebarrier assembly, float is accommodated via float spring 128, pulloutprotection is provided via barrier 114, and vertical movement of thetrailer and RIG is prevented by extension tip 126.

This arrangement may offer advantages over prior art vertically-movingrestraints because it detects the horizontal position of the RIGrelative to the barrier and adjusts the position of the barrier, ifnecessary, to help ensure a consistent horizontal relationship betweenthe two (i.e., that the RIG is in a preferred capture area, such thatany horizontal gap between the RIG and the barrier is minimized). Knownprior art vertically-moving restraints only detect the vertical positionof a RIG relative to the restraint (e.g., through use of a treadle platemounted on an upper surface of the restraint). Prior to the currentdisclosure, known vertically moving restraints provided no means foraddressing the problems associated with horizontal movement of thetrailer (and RIG).

FIG. 19 shows an example that is similar to that shown in FIGS. 16-18,but in this version, sliding cylinder 120 has been replaced bycompression spring 132. As in the previous examples, when the vehiclerestraint is actuated, lifting cylinder 110 is energized, causing it toextend. As lifting cylinder 110 extends, it exerts a force that has botha horizontal and a vertical component. The vertical force component isexerted against barrier assembly 104, whereas the horizontal forcecomponent is exerted against spring 132. Spring 132 has a springconstant that is sufficient to temporarily resist the horizontal forcecomponent exerted by lifting cylinder 110, thereby allowing the verticalforce component exerted on barrier assembly 104 to cause rollers 112 totravel upward within roller track 134. Barrier assembly 104 can beattached to rollers 112 such that barrier assembly 104 moves withrollers 112, as in previous examples. Barrier assembly 104 continues totravel upward until barrier 114 contacts RIG 20. Contact with RIG 20resists the vertical force component exerted by lifting cylinder 110 andprevents barrier assembly 104 from moving any further upward, therebycausing the pressure in lifting cylinder 110 to rise and the horizontalforce component to increase. Eventually, the horizontal force componentexerted by lifting cylinder 110 reaches a level that can no longer beresisted by spring 132 and spring 132 is compressed. As spring 132 iscompressed, sliding barrier 116 moves horizontally toward dock face 12until RIG sensor 118 contacts RIG 20. RIG sensor 118 is pivotallymounted to sliding barrier 116 and biased to the rest position shown inFIG. 16, such that continued horizontal movement of sliding barriertoward dock face 12 causes RIG sensor 118 to rotate until RIG sensorextension 122 actuates RIG sensor switch 124. Actuation of RIG sensorswitch 124 causes lifting cylinder 110 to cease extending, resulting inthe barrier assembly in its engaged position as shown in FIG. 19. As inthe example of FIGS. 16-18, RIG sensor 118 helps ensure that RIG 20 isconsistently and properly positioned relative to sliding barrier 116 andextension tip 126 (i.e., RIG 20 is in the preferred capture area, suchthat extension tip 126 extends over the top of at least a portion of theRIG). Furthermore, when the RIG is properly positioned relative to thebarrier assembly, float is accommodated via float spring 128, pulloutprotection is provided via barrier 114, and vertical movement of thetrailer and RIG is prevented by extension tip 126.

Although the invention is described with reference to various examples,it should be appreciated by those of ordinary skill in the art thatvarious modifications are well within the scope of the invention.Various cover panels, for instance, can be added to vehicle restraints16, 82 and 92 to provide a neater appearance, enclose electricalconnections, shelter working components from debris, and to coverpotential pinch points. Therefore, the scope of the invention is to bedetermined by reference to the following claims:

1. A method of operating a vehicle restraint disposed adjacent to aloading dock face, wherein the vehicle restraint includes a movablebarrier adapted to prevent movement of a RIG (rear impact guard) of avehicle in a direction opposite the loading dock face, wherein the RIGincludes a front surface and a rear surface, the rear surface beingcloser to the loading dock face than the front surface, the methodcomprising: moving the barrier to a first operative position wherein thebarrier is horizontally adjacent the front surface of the RIG; holdingthe barrier substantially stationary in the first operative position;and sensing that the front surface is no longer horizontally adjacentthe barrier.
 2. The method of claim 1, further comprising moving thebarrier at least horizontally toward the dock face to a second operativeposition, wherein the barrier is again horizontally adjacent the frontsurface, in response to sensing that the front surface is no longerhorizontally adjacent the barrier.
 3. The method of claim 1, furthercomprising illuminating a light in response to sensing that the frontsurface is no longer horizontally adjacent the barrier.
 4. The method ofclaim 1, further comprising sounding an audible alarm in response tosensing that the front surface is no longer horizontally adjacent thebarrier.
 5. The method of claim 1, wherein moving the barrier to thefirst operative position comprises moving the barrier in an upwarddirection and in a horizontal direction toward the loading dock face. 6.The method of claim 1, wherein moving the barrier to the first operativeposition comprises rotating the barrier.
 7. A method of operating avehicle restraint disposed adjacent to a loading dock face, wherein thevehicle restraint includes a rotatable barrier with a distal end, andthe rotatable barrier can be used for restricting a RIG (rear impactguard) of a vehicle, the method comprising: raising the distal end afterthe RIG has passed thereover; after raising the distal end, holding thedistal end substantially stationary relative to the RIG; and sensinghorizontal movement of the RIG away from the distal end.
 8. The methodof claim 7, further comprising moving the distal end vertically andhorizontally in response to sensing horizontal movement of the RIG. 9.The method of claim 7, wherein the raising of the distal end after theRIG has passed thereover is carried out by motorized rotation of therotatable barrier.
 10. The method of claim 7, further comprisingilluminating a light in response to sensing horizontal movement of theRIG.
 11. The method of claim 7, further comprising sounding an audiblealarm in response to sensing horizontal movement of the RIG.
 12. Avehicle restraint mountable near a loading dock for engaging a RIG (rearimpact guard) of a vehicle, the vehicle restraint comprising: a barrierthat is movable relative to the loading dock; a powered drive unitcoupled to the barrier such that the powered drive unit can move thebarrier; and a RIG sensor coupled to the barrier and providing a signalin response to the RIG's horizontal position relative to the barrier,such that the powered drive unit moves the barrier toward the RIG untilit receives the signal from the RIG sensor indicating that the barrieris horizontally adjacent the RIG, upon receiving the signal, the powereddrive unit is de-energized, and after the powered drive unit isde-energized, the signal triggers the powered drive unit to bere-energized to further move the barrier toward the RIG to minimize agap between the barrier and the RIG.
 13. The vehicle restraint of claim12, wherein the barrier comprises a rotating hook.
 14. The vehiclerestraint of claim 12, wherein the barrier comprises a verticallyelongate member.
 15. The vehicle restraint of claim 12, wherein thepowered drive unit is an electric motor.
 16. A vehicle restraintmountable near a loading dock for engaging a RIG (rear impact guard) ofa vehicle, wherein the RIG includes an upper surface, a lower surface, aleft lateral surface, and a right lateral surface that is closer to theloading dock than the left lateral surface, the vehicle restraintcomprising: a barrier assembly vertically movable relative to theloading dock; a RIG sensor coupled to the barrier assembly, the RIGsensor providing a signal in response to the RIG being in a preferredcapture area relative to the barrier assembly; and a powered drive unitcoupled to the barrier assembly such that the powered drive unit canmove the barrier assembly relative to the loading dock, the powereddrive unit being responsive to the signal such that: a) the powereddrive unit moves the barrier assembly toward the RIG until it receivesthe signal from the RIG sensor indicating that the RIG is positioned inthe preferred capture area, b) after receiving the signal, the powereddrive unit is de-energized, and c) after the powered drive unit isde-energized, the signal triggers the powered drive unit to bere-energized to further move the barrier assembly toward the RIG untilthe RIG is in the preferred capture area.
 17. The vehicle restraint ofclaim 16, wherein the preferred capture area is an area in which atleast a portion of the barrier assembly is below the lower surface,above the upper surface, and further from the dock face than the leftlateral surface.
 18. The vehicle restraint of claim 16, wherein thebarrier assembly comprises a rotating hook.
 19. The vehicle restraint ofclaim 16, wherein the barrier assembly comprises a vertical elongatemember with an upper tip that extends horizontally toward the loadingdock.
 20. The vehicle restraint of claim 16, wherein the powered driveunit is an electric motor.
 21. A vehicle restraint mountable to aloading dock for engaging a RIG (rear impact guard) of a vehicle,wherein the vehicle restraint includes a track mountable to the loadingdock and a track follower vertically movable along the track uponinteraction with the RIG, the vehicle restraint comprising: a barrierrotatably coupled to the track follower, wherein the barrier helpsdefine a RIG-receiving throat area in which the RIG may be positionedand the barrier includes a distal end and further defines a variablehorizontal distance between the distal end and the track; a RIG sensorcoupled to at least one of the track follower and the barrier, the RIGsensor providing a signal in response to the RIG's position relative tothe RIG-receiving throat area; and a powered drive unit coupled to thebarrier such that the powered drive unit can rotate the barrier relativeto the track follower between a blocking position and a stored position,the powered drive unit being responsive to the signal such that: a) thepowered drive unit rotates the barrier toward the RIG after the RIGforces the track follower downward, b) after rotating the barrier towardthe RIG, the powered drive unit is de-energized, and c) after thepowered drive unit is de-energized, the signal triggers the powereddrive unit to be re-energized to further rotate the barrier upward,thereby reducing the variable horizontal distance between the track andthe distal end of the barrier.
 22. The vehicle restraint of claim 21,further comprising a resilient member coupled to the track follower,wherein the resilient member urges the track follower upward.
 23. Thevehicle restraint of claim 21, further comprising a ramp disposed on thetrack follower and being engageable by the RIG such that the RIG canforce the track follower downward as the vehicle backs the RIG over theramp.
 24. The vehicle restraint of claim 21, wherein the barriercomprises a first plate and a second plate that define a spacetherebetween, and the RIG sensor is movable within that space.
 25. Thevehicle restraint of claim 21, wherein the powered drive unit is anelectric motor.
 26. The vehicle restraint of claim 21, furthercomprising a barrier sensor in addition to the RIG sensor, the barriersensor is coupled to at least one of the track follower and the barrier,the barrier sensor provides a stored-signal that triggers the powereddrive unit to stop lowering the barrier when the barrier reaches thestored position.
 27. The vehicle restraint of claim 21, wherein the RIGsensor includes a sensing arm pivotally coupled to the barrier such thatthe sensing arm can pivot into the RIG-receiving throat area.
 28. Thevehicle restraint of claim 21, wherein the RIG sensor includes anoptical beam that helps define the RIG-receiving throat area.
 29. Thevehicle restraint of claim 21, wherein the signal has a first state anda second state, the first state triggers the motor to be energized, andthe second state triggers the motor to be de-energized.
 30. The vehiclerestraint of claim 21, wherein when the RIG is captured by the barrierwithin the RIG-receiving throat area, and the RIG subsequently moves,the barrier responds by: translating upward under the impetus of theresilient member when the RIG moves upward, and rotates upward under theimpetus of the powered drive unit when the RIG moves horizontally towardthe track.